1. Field of the Invention
The present invention relates to a method of and an apparatus for adjusting a video tape running system in a deck mechanism of a video cassette recorder (VCR).
2. Description of the Prior Art
In general, such a tape running system of a VCR deck mechanism is adjusted to accord a relative position between a video tape passing through the system and a head drum so as to obtain a good picture quality. An audio head and a control head which are employed in the system are also adjusted to obtain good audio-quality and control signal.
Referring to FIGS. 1 to 3, a process for adjusting such a conventional VCR deck mechanism is illustrated. In fact, a tape running system in a deck mechanism of a video home system (VHS) VCR includes several mechanical components or elements for defining a tape passway through which a video tape 120 runs from a supply wheel 112 to a take-up reel 114 in a video tape cassette 110, as shown in FIG. 1. More particularly, the video tape 120 is supplied from the supply reel 112 to the take-up reel 114 through a tape inlet-side limit post P1, a slant post P2, a head drum 130, a tape outlet-side slant post P3, an audio and control (A/C) head assembly 140 and a limit post P4. The video tape 120 is guided by several guide posts 121, 122, 123, 125, 126 and 129, and controlled in speed by a capstan 127 and a pinch roller 128. Besides, as components for defining a tape runway through which the video tape 120 runs in the tape running system, there are a tension arm, an erasing head and the like. In running of the video tape, it is likely to be affected by the position of each of the components which forms the tape running system.
Substantially, such components which must be adjusted include shaped into a"-" head screw 210 or cross-head screw 220, or a hexagonal nut 220 or square nut 240. The audio and control head assembly 140 has a hexagonal nut 142 for adjusting a height of the head and an azimuth nut 144 for controlling an angle of the head.
The tape running system requires following conditions in order to be correctly operated.
1. Height condition: a height of a central line of the video tape from a reference plane must be even from an outlet point of the cassette to the inlet-side slant post and from an outlet-side slant post to an inlet point of the cassette. PA1 2. Parallelism condition: the video tape must be moved levelly on the tape runway course from an outlet of the cassette to an inlet-side slant post and from an outlet-side slant post to an inlet point of the cassette. PA1 3. Twist condition: the tape must be prevented from being twisted between the respective tape guide members. That is, when the tape is cut in wide direction, the tension acting on each points of the cut tape edge must be uniformed.
For these reasons, the tape running system is adjusted by determining the mechanical positions of each components so as to satisfy the above-mentioned conditions. In a case of the adjustment of the tape running system, it is considered that each components are modelled properly and the system is mechanically analyzed. But, a deviation in such modelling or analyzing is to be occurred whereby the system may be adjusted unstably. Mainly, the tape running system is adjusted to be stabilized so that a video signal and an audio signal are recorded or reproduced onto or from the video tape satisfactorily. In fact, an accurate adjustment is checked by way of several measuring methods to determine the stabilization of the system. For such measuring methods, a test tape having a specific signal recorded thereon is used in the deck mechanism so as to determine that the signal obtained from the test tape is within a predetermined value.
Such measuring methods are as bellows:
* 2H test tape method:
A sinusoidal wave form signal having a constant frequency of approximately 4 MHz is recorded on a video signal area of the video tape and also a sinusoidal wave signal having a constant frequency and an amplitude is recorded on an audio signal area of the tape. Further, pulses of 30 Hz are recorded on a control signal area of the video tape to match a synchronism of the video signal. According to this method, such an adjustment is estimated on the basis of linearity of an envelope waveform obtained from the video signal and an amplitude of the audio signal.
** CTL test tape method:
A control pulse signal is recorded on a control signal area in a magnitude ratio of 1: 2 and a signal ratio between two peak points of the reproduced signal is checked to determine the adjusted state of the tape running system. An audio signal is also recorded to determine a suitability of the audio signal.
*** 6H test tape method:
This method is very similar to the 2H test tape in signal format. In the 6H test tape method, however, a signal is recorded under a triple-speed recording mode so as to check a suitable reproduction possibility of a video tape having a signal recorded thereon under a triple-speed recording mode.
As shown in FIG. 2, each of the P1, P2, P3 and P4 posts has a screw-head 210 oil which linear groove is formed except a central portion. A screw driver for driving the screw 210 has a shape, shown in FIG. 5 as indicated 340, corresponding to the screw 210 to be suitably fitted with the screw 210.
The audio and control head assembly has a height control nut 144 and an azimuth screw at the head is adjusted in height, and an height and azimuth adjustment are carried out by way of a hexagonal nut and the azimuth control screw, respectively. A degree of slant of the audio and control head is also adjusted by the height control nut.
In the adjustment of the tape running system, lower ends of the tape pass of the P1 and P4 posts are aligned with a height of 90 degree phase lead line of the head drum. An envelope waveform reproduced from the 2H test tape is displayed on an oscilloscope, and the P2 and P3 posts are adjusted to produce a smooth signal. Thereinafter, while reproducing the CTL test tape, the audio and control head assembly 140 is adjusted with the height nut 144 thereof to satisfy a signal ratio of 1: 2 and the azimuth control screw 142 do the audio and control head assembly is adjusted to obtain an audio signal is produced to a desired amplitude.
Next, the 6H test tape is reproduced in the triple-speed reproduction mode to check the condition of the audio and control head assembly adjusted. In this process, such adjustment can be perfectly completed over an additional adjusting process carried out by a skilled worker.
According to such a adjustment for a conventional tape running system, the posts P1, P2, P3 and P4, the audio and control head height control nut and the azimuth control screw are manually adjusted so as to achieve a good reproduction of a video signal, an audio signal and a control signal which form a VCR signal. As a result, in the conventional adjusting method, it is difficult to make an accurate and quick adjustment of the tape running system, and a quality in adjustment corresponds upon a degree of skill of a worker.